Commit c571b72e authored Dec 10, 2019 by Davidlohr Bueso Committed by Ingo Molnar Dec 11, 2019

Revert "locking/mutex: Complain upon mutex API misuse in IRQ contexts"



This ended up causing some noise in places such as rxrpc running in softirq.

The warning is misleading in this case as the mutex trylock and unlock
operations are done within the same context; and therefore we need not
worry about the PI-boosting issues that comes along with no single-owner
lock guarantees.

While we don't want to support this in mutexes, there is no way out of
this yet; so lets get rid of the WARNs for now, as it is only fair to
code that has historically relied on non-preemptible softirq guarantees.
In addition, changing the lock type is also unviable: exclusive rwsems
have the same issue (just not the WARN_ON) and counting semaphores
would introduce a performance hit as mutexes are a lot more optimized.

This reverts:

    a0855d24: ("locking/mutex: Complain upon mutex API misuse in IRQ contexts")

Fixes: a0855d24: ("locking/mutex: Complain upon mutex API misuse in IRQ contexts")
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Tested-by: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-afs@lists.infradead.org
Cc: linux-fsdevel@vger.kernel.org
Cc: will@kernel.org
Link: https://lkml.kernel.org/r/20191210220523.28540-1-dave@stgolabs.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 1a365e82

kernel/locking/mutex.c

+0 −4

Original line number	Diff line number	Diff line
		@@ -733,9 +733,6 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
		*/
		void __sched mutex_unlock(struct mutex *lock)
		{
		#ifdef CONFIG_DEBUG_MUTEXES
		WARN_ON(in_interrupt());
		#endif
		#ifndef CONFIG_DEBUG_LOCK_ALLOC
		if (__mutex_unlock_fast(lock))
		return;
		@@ -1416,7 +1413,6 @@ int __sched mutex_trylock(struct mutex *lock)

		#ifdef CONFIG_DEBUG_MUTEXES
		DEBUG_LOCKS_WARN_ON(lock->magic != lock);
		WARN_ON(in_interrupt());
		#endif

		locked = __mutex_trylock(lock);

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